1. Technical Field
Embodiments of the invention relate generally to computer platform hibernate and resume.
2. Background Art
Computer systems typically have certain low power states referred to as S-states including S3 and S4. S3 is sometimes referred to as Standby, Sleep, or Suspend to RAM. State S3 is a sleep state in which the operating system (OS) saves its context into physical memory (dynamic random access memory (DRAM)) and puts the system into a suspend state. Open documents and programs (applications) that were used at the time of entering into S3, or at least a portion of the programs are also saved in DRAM during the suspend state. Contents of some chipset registers may also be written to DRAM. The physical memory DRAM is sometimes called main memory or system memory. During this suspend state, all power is removed from the platform hardware with the exception of the DRAM and a small amount of circuitry used to later wake the system. The S3 power state provides a relatively fast suspend and resume (wake) time due to its ability to save and restore OS context and previously used programs and documents from hi-speed DRAM memory.
S4 is sometimes referred to as Hibernate, Safe Sleep, or Suspend to disk. In S4, the OS context and open documents and programs (or a portion thereof) are saved on a hard disk drive (HDD) rather than in fast DRAM memory. This allows for higher power savings than the S3 state because the DRAM is not kept powered. However, there are higher latencies due to slow read and write access times of the HDD. Typical S4 hibernate and resume times are in the order of 10 s of seconds.
While 10 s of seconds may not seem like much time in general, for a user waiting for his or her computer to hibernate or resume from hibernation, it can seem like a long time. Further, while the amount of power needed to keep DRAMs operational is not much for a short amount of time, it can have a significant effect on the charge in a battery over a longer amount of time.
Accordingly, there is a need for circuitry and techniques that provides faster hibernate and resume times than are provided with the S4 power state, and that consumes less power than the S3 power state.